Adhesive sheet for laser dicing and its manufacturing method

ABSTRACT

An adhesive sheet for laser dicing is used for dicing a workpiece into individual chips by light absorption ablation of laser beam and has at least an adhesive layer on one side of a base material which has a surface opposite to the adhesive layer having no convex parts of width (W) of 20 mm or less and height (h) of 1 μm or more, or no concave parts of width (W) of 20 mm or less and depth (d) of 1 μm or more.

CROSS-REFERENCE TO PRIORITY APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 11/054,795, filed Feb. 10, 2005, which claims priority toJapanese Patent Application No. 2004-44188, filed Feb. 20, 2004. Thedisclosures of the above-referenced applications are incorporated byreference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an adhesive sheet for laser dicing usedfor supporting and fixing a workpiece when forming a reformed regioninside the workpiece by light absorption ablation of laser beam andseparating into individual pieces. The invention also relates to amanufacturing method of small pieces of element by separating intoindividual chips by light absorption ablation of laser beam by usingvarious workpieces, such as circuit board, semiconductor wafer, glasssubstrate, ceramic substrate, metal substrate, light emitting ordetecting element board of semiconductor laser, MEMS substrate, andsemiconductor package.

2. Description of the Related Art

In manufacturing process of semiconductor related products, variouscircuits are formed on a substrate, and the surface is treated, and thenthe semiconductor substrate and the like is cut and separated (diced) tomanufacture small pieces of element (for example, semiconductor devices,etc.). Specifically, an adhesive sheet is glued to the substrate, thesubstrate is diced by using a blade, and the adhesive sheet is expandedto separate into small pieces of element.

Recently, causing a little heat damage, the dicing method ofsemiconductor substrate by light absorption ablation by laser beamcapable of processing at high precision is noticed as precise cuttingmethod.

Technically, for example, a method is proposed for supporting and fixinga workpiece on a dicing sheet, and dicing the workpiece by laser beam(Japanese unexamined patent publication No. 2002-343747). The dicingsheet is composed of a base material including a support sheet, and anadhesive layer disposed at one side surface of the base material, andthe adhesive layer can be cut off by laser beam, and the support sheetcannot be cut by laser beam.

Other method is proposed for dicing a semiconductor wafer by combiningwater microjet and laser (Japanese unexamined patent publication No.2003-34780). On one side of a base material, a non-radiation curing typeadhesive layer and a radiation curing type adhesive layer are disposed,and the base material allows to pass jet water stream of water jet, andthe non-radiation curing type adhesive layer is interposed between thebase material and the radiation curing type adhesive layer, according tothis adhesive tape for laser dicing.

A further proposal is a laser processing method comprising a step offixing a workpiece to be processed on a sheet of an adhesive surface,and a step of emitting laser beam by focusing on a spot inside theworkpiece to be processed, and forming a reformed region inside theworkpiece to be processed along an intended cutting line of theworkpiece (Japanese unexamined patent publication No. 2003-33887).

When emitting laser beam, in order to form a reformed region at auniform height inside the workpiece (the workpiece to be processed), itis required to focus the laser beam precisely in the intended area. Indicing by using an ordinary blade, thickness fluctuations of theworkpiece of about several microns do not matter, but in the case oflaser dicing, thickness fluctuations of the workpiece of about severalmicrons may cause to deviate the focusing region of laser beam, andheight of reformed region is not uniform, and height fluctuations in thereformed region may make it difficult to separate the workpiece intoindividual chips.

A certain laser dicing apparatus is equipped with a height adjustingmechanism, and the problem as described above may be solved by usingsuch apparatus, but it takes much time in fine adjustment of height, andthe production efficiency is poor, and it is not practicable. Aworkpiece having a large curvature may be machined somewhat by the laserdicing apparatus, but a workpiece having small undulations cannot bemachined by the laser dicing apparatus.

Further, when separating into chips by expanding, depending on theadhesive sheet to be used, only the peripheral area of the sheet isexpanded and the central area of the sheet is not expanded sufficiently,the central chips may not be separated neatly into individual pieces.

SUMMARY OF THE INVENTION

It is hence an object of the invention to present an adhesive sheet forlaser dicing capable of dicing the workpiece into individual chipssecurely at high production efficiency when forming a reformed regioninside the workpiece by light absorption ablation of laser beam, and itsmanufacturing method. It is also an object of the invention to present amethod of manufacturing small pieces of element securely at highproduction efficiency by using the adhesive sheet for laser dicing.

The inventor has accumulated intensive studies to solve the problems,and has discovered that the objects can be achieved by using theadhesive sheet for laser dicing (hereinafter called adhesive sheet)described below, thereby completed the invention.

That is, the invention relates to an adhesive sheet for laser dicing,being an adhesive sheet for laser dicing used for dicing into individualchips by forming a reformed region inside of a workpiece by lightabsorption ablation of laser beam, in which the adhesive sheet has anadhesive layer at least on one side of a base material, and at least thebase material surface not contacting with the adhesive layer is freefrom convex parts of width (W) of 20 mm or less and height (h) of 1 μmor more, and concave parts of width (W) of 20 mm or less and depth (d)of 1 μm or more.

The adhesive sheet is laminated to the attraction stage side (laser beamexit side) or laser beam incident side of a workpiece before laserprocessing of workpiece by light absorption ablation of laser beam, andis used for supporting and fixing the workpiece (small pieces ofelement) in dicing and subsequent respective processes.

The inventor has estimated the cause of failure of dicing the workpieceinto individual chips to be present in the adhesive sheet used forsupporting and fixing the workpiece. As discovered by the inventor, ifthe base material surface of the adhesive sheet has convex parts ofwidth (W) of 20 mm or less and height (h) of 1 μm or more, or concaveparts of width (W) of 20 mm or less and depth (d) of 1 μm or more, whenthe adhesive sheet is glued to the workpiece, the flatness of theworkpiece may be disturbed by the effects of undulations, and thefocusing region of laser beam may be deviated, and the height of thereformed region formed inside the workpiece is uneven, and thereby theworkpiece cannot be diced neatly into individual chips.

Such undulations are considered to be formed in the manufacturingprocess of adhesive sheet. For example, in heat treatment process forstabilizing the characteristics of the adhesive, the base materialpartly shrinks to form undulations. Or in the process of heating ofrolled laminated sheet (adhesive sheet) or storing the adhesive sheet inrolled state, the base material surface not contacting with the adhesivelayer adheres to the smooth separator for protecting the surface ofadhesive layer, and as pressure is applied to the separator, the basematerial is deformed to form undulations.

FIG. 1 is a schematic diagram showing a section of adhesive sheet of theinvention. As shown in FIG. 1, the width (W) of convex part is themaximum interval (mm) from the start point to end point of convex part,and the width (W) of concave part is the maximum interval (mm) from thestart point to end point of concave part. The height (h) of convex partis the maximum height (μm) of convex part from the base materialsurface, and the depth (d) of concave part is the maximum depth (μm) ofconcave part from the base material surface.

The adhesive sheet of the invention is required to be free from suchconvex parts and concave parts of width (W) of 20 mm or less on the basematerial surface. If convex parts or concave parts exceeding the width(W) of 20 mm are present on the base material surface, by using thelaser dicing apparatus with height adjusting mechanism, the apparatuscan sufficiently correspond to height changes of the workpiece flexible,and there is no problem.

In the adhesive sheet of the invention, the adhesive agent for formingthe adhesive layer is preferred to be a radiation curing type adhesive.When using a radiation curing type adhesive, the adhesiveness of theadhesive layer is lowered by irradiation with radiation (for example,ultraviolet ray), and therefore after emitting radiation to the adhesivelayer after forming a reformed region, the adhesive sheet can be peeledoff easily.

Also in the adhesive sheet of the invention, the base material ispreferred to be free from necking property. The necking property is anature of elongating depending on the stress until rupture in tensilestrength test. When dicing into individual chips by expanding, in thecase of a base material having necking property, only the stressedportion is expanded, and the stress is not applied uniformly to theentire base material, and the central area is not diced into individualchips. As a material free from necking properly, in particular, it ispreferred to use polyvinyl chloride.

In the adhesive sheet of the invention, preferably, a separator isdisposed on the adhesive layer. By using the separator, the laminatedsheet (adhesive sheet) can be heated or stored in roll. Or, before useof adhesive sheet, the surface of the adhesive layer can be protectedfrom dust and foreign matter.

The invention relates to a manufacturing method of adhesive sheet forlaser dicing characterized by not heating a laminated sheet having atleast an adhesive layer on one side of a base material. Without heattreatment of laminated sheet, partial deformation of base material byheat can be prevented, and hence formation of undulations on the basematerial surface can be suppressed.

The invention relates also to a manufacturing method of adhesive sheetfor laser dicing comprising a step of disposing an adhesive layer on oneside of a base material, a step of fabricating a laminated sheet bystacking a separator on the adhesive layer, a step of fabricating arolled laminated sheet by taking up the laminated sheet in roll, and astep of heating the rolled laminated sheet.

The arithmetic average height Ra of the surface of the base material notcontacting with the adhesive layer is preferred to be 0.4 μm or more.When the laminated sheet is taken up in roll, the surface of the basematerial and the surface of the separator contact with each other, butif the surface of the base material is too smooth (Ra is less than 0.4μm), the base material tightly contacts with the separator surface anddoes not slide smoothly. When the rolled laminated sheet is heated insuch state, not only the base material shrinks, but also a pressure isapplied to the separator, and lots of local undulations tend to beformed on the base material surface. Besides, if the surface of the basematerial is too smooth, the frictional force of base material andattraction stage increases, and expanding is not uniform, and hence theworkpiece cannot be easily diced into individual chips.

The surface of the separator not contacting with the adhesive layer ispreferred to be in sprinkled or rough structure. When taking up thelaminated sheet in roll, when the surface of the separator contactingwith the base material is in sprinkled or rough structure, the contacttightness with the base material surface is lessened, the slidingperformance of the base material may be enhanced. As a result, if thebase material shrinks by heat treatment, since the sliding performanceof the base material and separator is excellent, local deformation issuppressed, and local formation of undulations on the base materialsurface can be prevented.

The invention further relates to a manufacturing method of small piecesof element comprising a step of adhering an adhesive layer of adhesivesheet for laser dicing to one side of a workpiece, a step of forming areformed region in the workpiece by emitting laser beam, a step ofdicing the workpiece into individual chips by expanding the adhesivesheet for laser dicing, and a step of peeling off the adhesive sheet forlaser dicing from the separated workpiece.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing a section of adhesive sheet forlaser dicing of the invention.

FIG. 2 is a schematic diagram showing an example of dicing method ofsemiconductor wafer.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Laser used in the invention is not particularly specified as far as areformed region can be formed in the workpiece by multiple photonabsorption, and usable examples include YAG laser of transmissionwavelength of 1064 nm, YVO₄ laser, YLF laser, and titanium sapphirelaser. A proper type of laser can be selected depending on the materialof the workpiece. For example, for silicon wafer, it is preferred to useYAG laser.

The workpiece is not particularly limited as far as a reformed regioncan be formed in the workpiece by light absorption ablation of laserbeam emitted from the laser, and examples include sheet material,circuit board, semiconductor wafer, glass substrate, ceramic substrate,metal substrate, light emitting or detecting element board ofsemiconductor laser, MEMS (micro-electromechanical system) board, andsemiconductor package.

The adhesive sheet for laser dicing of the invention can be preferablyused in laser dicing of semiconductor wafer, in particular.

The sheet material includes, for example, high polymer films andnonwoven cloths made of polyimide resin, polyester resin, epoxy resin,urethane resin, polystyrene resin, polyethylene resin, polyamide resin,polycarbonate resin, silicone resin, fluorine resin, and others, sheetshaving physical or optical function by drawing process or impregnatingprocess of these resins, metal sheets of copper, aluminum, stainlesssteel or the like, or the high polymer films and/or metal sheetslaminated directly or by way of adhesive or the like.

The circuit board includes one-side or both-side multilayer flexibleprinted board, rigid board of glass epoxy, ceramic, or metal core board,optical circuit formed on glass or polymer, and photo-electric mixedcircuit board.

An adhesive sheet 4 of the invention has at least an adhesive layer 2 onone side of a base material 1 as shown in FIG. 1. To take up thelaminated sheet in roll, a separator 3 may be disposed on the adhesivelayer 2.

The forming material of a base material includes, for example,polyethylene terephthalate, polyethylene naphthalate, polystyrene,polycarbonate, polyimide, (meth)acrylic polymer, polyurethane resin,polynorbornene resin, polyethylene glycol, polytramethylene glycol,other polyalkylene glycol resin, silicone rubber, polyethylene,polypropylene, polybutadiene, polyvinyl alcohol, ethylene-vinyl acetatecopolymer (EVA), polymethyl pentene, polyvinyl chloride, and otherpolyolefin resins, but is not limited to these examples alone.

Above all, it is preferred to use a polymer free from necking property,and examples of such polymer include, among others, polybutadiene, EVA,polyvinyl chloride, other polymers having rubber elasticity,alpha-olefin polymer, and others. In particular, the base material ispreferred to be formed of soft vinyl chloride.

The base material may be either single layer or plural layers.

The thickness of the base material may be properly adjusted within arange not sacrificing the handling property or working efficiency ineach process, such as gluing to the workpiece, laser dicing ofworkpiece, and peeling and collection of small pieces of element, andusually it is about 50 to 300 μm, or preferably 50 to 150 μm. One sideof the base material may be treated, for example, by common surfacetreatment for enhancing the adhesion or holding property to the adhesivelayer, such as chromate treatment, ozone exposure, flame exposure, highvoltage electric shock exposure, ionization radiation treatment, otherchemical or physical treatment, or coating treatment by undercoat paint(for example, by adhesive substance mentioned below). The arithmeticaverage height Ra of the surface of other side of the base material ispreferred to be 0.4 μm or more, and more preferably 0.5 μm or more.However, to prevent formation of undulations, the arithmetic averageheight Ra is preferred to be 1 μm or less, and more preferably 0.9 μm orless.

Forming materials of adhesive layer include known adhesive materialsincluding (meth)acrylic polymer and rubber polymer.

Monomer components for forming (meth)acrylic polymer are alkyl(meth)acrylates having alkyl radical of straight chain or branch chainwith 30 carbon atoms or less, or preferably 4 to 18 carbon atoms,including, for example, methyl radical, ethyl radical, n-propyl radical,isopropyl radical, n-butyl radical, t-butyl radical, isobutyl radical,amyl radical, isoamyl radical, hexyl radical, heptyl radical, cyclohexylradical, 2-ethyl hexyl radical, octyl radical, iso-octyl radical, nonylradical, isononyl radical, decynol radical, isodecyl radical, undecylradical, lauryl radical, tridecyl radical, tetradecyl radical, stearylradical, octadecyl radical, and dodecyl radical. These alkyl(meth)acrylates may be used either alone or in combination of two ormore types.

In order to modify the adhesiveness, coagulation or heat resistance of(meth)acrylic polymer, other monomer components than mentioned above maybe copolymerized as required. Other monomers capable of forming suchpolymers include, for example, acrylic acid and methacrylic acid,carboxyethylacrylate and carboxypentylacrylate, itaconic acid and maleicacid, fumaric acid and crotonic acid or other monomer containingcarboxyl radical, maleic anhydride and itaconic anhydride or othermonomer of acid anhydride, (meth)acrylic acid 2-hydroxylethyl and(meth)acrylic acid 2-hydroxyl propyl, (meth)acrylic acid 4-hydroxylbutyl and (meth)acrylic acid 6-hydroxylhexyl, (meth)acrylic acid8-hydroxyoctyl and (meth)acrylic acid 10-hydroxyl decyl, (meth)acrylicacid 12-hydroxylauryl and (4-hydroxymethyl cyclohexyl)-methylacrylate orother monomer containing hydroxyl radical, styrene sulfonic acid andacrylic sulfonic acid, 2-(meth)acrylic amide-2-methyl propane sulfonicacid and (meth)acrylic amide propane sulfonic acid, sulfopropyl(meth)acrylate and (meth)acryloyl oxynaphthalene sulfonic acid or othermonomer containing sulfonic acid radical, 2-hydroxy ethyl acryloylphosphate or other monomer containing phosphoric acid radical,(meth)acrylic amide, (meth)acrylic acid N-hydroxymethyl amide,(meth)acrylic acid alkyl aminoalkyl ester (for example, dimethylaminoethyl methacrylate), t-butyl aminoethyl methacrylate, etc.),N-vinyl pyrrolidone, acryloyl morphorine, vinyl acetate, styrene,acrylonitrile, etc. These monomer components may be used either alone orin combination of two or more types.

In addition, for the purpose of crosslinking of (meth)acrylic polymer orthe like, multifunctional monomers and the like may be added as requiredas monomer component for copolymerization.

Examples of such monomer include hexanediol di(meth)acrylate,(poly)ethyleneglycol di(meth)acrylate, (poly)propyleneglycoldi(meth)acrylate, neopentylglycol di(meth)acrylate, pentaerythritoldi(meth)acrylate, trimethylolpropane tri(meth)acrylate,tetramethylolmethane tetra(meth)acrylate, pentaerythritoltri(meth)acrylate, pentaerythritol tetra(meth)acrylate,dipentaerythritol monohydroxypenta(meth)acrylate, dipentaerythritolhexa(meth)acrylate, epoxy (meth)acrylate, polyester (meth)acrylate,urethane (meth)acrylate, and others. One type or two or more types ofmultifunctional monomer may be used.

The content of multifunctional monomer is preferred to be 30 wt % orless of the total monomer content from the viewpoint of adhesiveness andothers, and more preferably 15 wt % or less.

To prepare (meth)acrylic polymer, various methods may be applied, forexample, solution polymerization method of mixture containing one, twoor more types of monomer components, emulsification polymerizationmethod, block polymerization, and suspension polymerization method.

Polymerization initiator includes peroxides such as hydrogen peroxide,benzoyl peroxide, and t-butyl peroxide. It is preferred to use alone,but it may be combined with reducer to be used as redox polymerizationinitiator. The reducer includes sulfite, hydrogen sulfite, iron, copper,cobalt salt, or other ionized salt, triethanolamine and other amines,aldose, ketose, and other reducing sugar. An azo compound is also apreferred polymerization initiator, and its example includes2,2′-azobis-2-methylpropio amidinate, 2,2′-azobis-2,4-dimethylvaleronitrile, 2,2′-azobis-N,N′-dimethylene isobutyl amidinate,2,2′-azobis isobutyronitrile, and 2,2′-azobis-2-methyl-N-(2-hydroxyethyl) propione amide. Two or more types of these polymerizationinitiators may be used in combination.

Reaction temperature is usually about 50 to 85° C., and the reactiontime is about 1 to 8 hours. Among the manufacturing method, solutionpolymerization is preferred, and as solvent of (meth)acrylic polymer,generally, ethyl acetate, toluene, and other polar solvents are used.The solution concentration is generally about 20 to 80 wt %.

The adhesive agent may be properly combined with a crosslinking agentfor raising the number-average molecular weight of (meth)acrylic polymerused as base polymer. Examples of crosslinking agent includepolyisocyanate compound, epoxy compound, aziridine compound, melamioneresin, urea resin, anhydrous compound, polyamine, and polymer containingcarboxyl radical. When the crosslinking agent is used, its content mustbe determined so that the peel adhesive strength may not be lowered toomuch, and generally it is preferred to add by about 0.01 to 5 parts byweight in 100 parts by weight of base polymer. The adhesive agent forforming the adhesive layer may be also combined with other knownadditives as required, in addition to the specified components, such asadhesion improver, aging retardant, filler, coloring matter, and others.

To improve peeling from workpiece, the adhesive agent is preferred to beradiation curing type adhesive which is cured by radiation such asultraviolet ray or electron ray. When a radiation curing type adhesiveis used as the adhesive agent, since the adhesive layer is irradiatedwith radiation after laser processing, the base material is preferred tohave a sufficient radiation transmissivity.

The radiation curing type adhesive is not particularly limited as far asit is adhesive and has a radiation curing functional group such ascarbon-carbon double bond. As the radiation curing type adhesive, forexample, a radiation curing type adhesive blending radiation curingmonomer component or oligomer component to the above (meth)acrylicpolymer may be used.

Examples of monomer component or oligomer component of radiation curingtype to be blended include urethane; (meth)acrylate oligomer,trimethylol propane tri(meth)acrylate, tetramethylol methanetetra(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritoltetra(meth)acrylate, dipentaerythritol monohydroxy penta(meth)acrylate,dipentaerythritol hexa(meth)acrylate, 1,4-butylene glycoldi(meth)acrylate, and others. One type or two or more types of monomercomponent or oligomer component may be used.

The blending amount of radiation curing monomer component or oligomercomponent is not particularly specified, but considering theadhesiveness, it is preferred to add by about 5 to 500 parts by weightin 100 parts by weight of base polymer such as (meth)acrylic polymer forcomposing the adhesive agent, and more preferably by about 60 to 150parts by weight.

As the radiation curing type adhesive, further, a base polymer havingcarbon-carbon double bond in the polymer side chain, main chain or mainchain end may be used. Such base polymer is preferred to have(meth)acrylic polymer as basic skeleton. In this case, radiation curingtype monomer component or oligomer component may not be added, and itsuse is free.

The radiation curing type adhesive should contain a photopolymerizationinitiator when curing by ultraviolet ray or the like. Examples ofphotopolymerization initiator include4-(2-hydroxyethoxy)phenyl(2-hydroxy-2-propyl) ketone, α-hydroxy-α,α-methyl acetophenone, methoxy acetophenone, 2,2-dimethoxy-2-phenylacetophenone, 2,2-diethoxy acetophenone, 1-hydroxy cyclohexyl phenylketone, 2-methyl-1-[4-(methylthio)-phenyl]-2-morpholinopropane-1, otheracetophenone compounds, benzoin ethyl ether, benzoin isopropylether,anizoin methyl ether, other benzoin ether compounds,2-methyl-2-hydroxypropylphenone, other α-ketol compounds, benzyldimethyl ketal, other ketal compounds, 2-naphthalene sulfonyl chloride,other aromatic sulfonyl chloride compounds,1-phenone-1,1-propanedione-2-(o-ethoxy carbonyl) oxime, otherphotoactive oxime compounds, benzophenone and benzoyl benzoic acid,3,3′-dimethyl-4-methoxybenzophenone, other benzophenone compounds,thioxanthone, 2-chlorothioxanthone, 2-methyl thioxanthone, 2,4-dimethylthioxanthone, isopropyl thioxanthone, 2,4-dichlorothioxanthone,2,4-diethyl thioxanthone, 2,4-diisopropyl thioxanthone, otherthioxanthone compounds, and also camphor quinone, ketone halide, acylphosphino oxide, acyl phosphonate, etc.

The content of photopolymerization initiator is preferred to be about0.1 to 10 parts by weight in 100 parts by weight of base polymer such as(meth)acrylic polymer for composing the adhesive agent, or morepreferably about 0.5 to 10 parts by weight.

The adhesive sheet for laser dicing of the invention may be manufacturedby applying an adhesive solution to the surface of the base material,drying (heating and crosslinking as required), and forming an adhesivelayer. In other method, an adhesive layer is formed on a peeling liner,and it is glued to a base material.

The adhesive layer is preferred to be low in content of low molecularsubstance from the viewpoint of prevention of contamination onworkpiece. From such point of view, the number-average molecular weightof (meth)acrylic polymer is preferred to be 300,000 or more, morepreferably 400,000 to 3,000,000.

The thickness of adhesive layer may be properly selected within a rangenot peeling from the workpiece, and is preferred to be about 4 to 50 μm,more preferably about 5 to 20 μm.

The adhesive strength of adhesive layer is preferred to be 20 N/20 mm orless on the basis of adhesive strength (90-degree peel value, peelingspeed 300 mm/min) at ordinary temperature (before laser emission) onSUS304, and more preferably 0.001 to 10 N/20 mm, or further preferably0.01 to 8 N/20 mm.

On the surface of adhesive layer of adhesive sheet for laser dicing ofthe invention, it is preferred to dispose a separator for protecting theadhesive layer for labeling, or for the ease of heat treatment orstorage by taking up the laminated sheet in roll.

The separator forming material includes polyether ether ketone,polyether imide, polyallylate, polyethylene naphthalate, polyethylenefilm, polypropylene film, polybutene film, polybutadiene film,polymethyl pentene film, polyvinyl chloride film, vinyl chloridecopolymer film, polyethylene terephthalate film, polybutyleneterephthalate film, polyurethane film, ethylene-vinyl acetate copolymerfilm, ionomer resin film, ethylene-(meth)acrylic acid copolymer film,ethylene-(meth)acrylate ester copolymer film, polystyrene film,polycarbonate film, and other plastic films.

One side of the separator may be treated for enhancing the peelingproperty from the adhesive layer, as required, by silicone process,long-chain alkyl process, fluorine process, or other peeling process.Further, as required, ultraviolet transmission preventive treatment maybe applied to prevent reaction of adhesive sheet for laser dicing byenvironmental ultraviolet ray. The thickness of the separator is usuallyabout 5 to 200 μm, preferably 25 to 100 μm, and more preferably 38 to 60μm.

The surface of the separator not contacting with the adhesive layer ispreferred to be in sprinkled or rough structure. These shapes can beformed by sand blasting or chemical etching. The separator can be alsoformed by using metal roll or rubber roll. The arithmetic average heightRa of the surface of the separator not contacting with the adhesivelayer is preferred to be 0.2 to 2 μm, and more preferably 0.3 to 1.5 μm.If the arithmetic average height Ra is less than 0.2 μm, when thelaminated sheet (adhesive sheet) is taken up in roll, the adhesion withthe surface of base material increases, and the base material is likelyto be integrated with the separator. When the rolled laminated sheet isheated in such state, not only the base material shrinks, but also apressure is applied to the separator, and lots of local undulations tendto be formed on the base material surface. On the other hand, when thearithmetic average height Ra is more than 2 μm, convex part and concavepart shapes of the separator are transferred on the base materialsurface, and convex parts of more than 1 μm in height (h) or concaveparts of more than 1 μm in depth (d) may be formed on the base materialsurface.

The laminated sheet having a separator on the adhesive layer ispreferred to be heated in rolled state. By heating the laminated sheet,the characteristics of the adhesive can be stabilized. In heattreatment, the temperature is in a range of 30 to 60° C., and thetreatment time is about 12 to 100 hours. The adhesive sheet thusmanufactured is free from convex parts of width (W) of 20 mm or less andheight (h) of 1 μm or more, and concave parts of width (W) of 20 mm orless and depth (d) of 1 μm or more, at least on the base materialsurface not contacting with the adhesive layer.

A manufacturing method of small pieces of element by light absorptionablation of laser beam by using the adhesive sheet is explained below.

In the case of laser dicing process of semiconductor wafer, as shown inFIG. 2, one side of semiconductor wafer 5 is glued to the adhesive sheet4 disposed on the attraction stage 6, and the laser beam 7 emitted froma specified laser oscillator is focused to illuminate the inside of thesemiconductor wafer 5 by a lens, and the laser illuminated position ismoved along the specified processing line, so that a reformed region isformed inside the semiconductor wafer 5. The laser beam moving means isrealized by any known laser processing method, such as galvano scan, X-Ystage scan, mask, or imaging process. A protective sheet 8 may beprovided at the laser beam incident side of the semiconductor wafer 5.

After forming a reformed region in the semiconductor wafer, by expandingthe adhesive sheet, the semiconductor wafer is cut from the reformedregion, and adjacent small pieces of element (semiconductor chips) arebroken apart. Then, by the known die bonder or similar device, the smallpieces of element are picked up by using a poking pin known as needle,or the small pieces of element are picked up and collected by knownmethod such as the method disclosed in Japanese patent publication No.2001-118862.

In the manufacturing method of small pieces of element of the invention,after dicing into small pieces of element by expanding, the adhesivesheet 4 is peeled off, and the small pieces of element are collected.The peeling method is not particularly specified, but it is importantnot to apply stress to cause permanent deformation of small pieces ofelement at the time of peeling. For example, when a radiation curingtype adhesive is used for the adhesive layer 2 of the adhesive sheet 4,radiation is applied depending on the material of the adhesive agent,and the adhesive layer is cured and the adhesiveness is lowered. Byapplication of radiation, the adhesiveness of the adhesive layer islowered by curing, and it is peeled easily. Application means ofradiation is not specified, and, for example, ultraviolet ray may beapplied.

EXAMPLES

The invention is described below by referring to preferred examples, butthe invention is not limited to these examples alone.

[Measurement of Number-Average Molecular Weight]

Number-average molecular weight of synthesized (meth)acrylic polymer wasmeasured in the following method. The synthesized (meth)acrylic polymerwas dissolved in THF at 0.1 wt. %, and the number-average molecularweight was measured by converting into polystyrene by using GPC (gelpermeation chromatography). The measuring conditions are as follows.

-   -   GPC apparatus: HLC-8120GPC of TOSOH CORPORATION    -   Column: (GMH_(HR)-H)+(GMH_(HR)-H)+(G2000H_(HR)), of TOSOH        CORPORATION    -   Flow rate: 0.8 mL/min    -   Concentration: 0.1 wt. %    -   Injection volume: 100 μL    -   Column temperature: 40° C.    -   Eluate: THF        [Measurement of Arithmetic Average Height (Ra)]

Measured according to JIS B 0601-2001. The measuring apparatus was P-11(contact type) of Tencor Corporation.

Example 1

In ethyl acetate, 70 parts by weight of methyl acrylate, 30 parts byweight of butyl acrylate, and 5 parts by weight of acrylic acid werecopolymerized, and a solution containing acrylic polymer ofnumber-average molecular weight of 800,000 was obtained. In thissolution, 60 parts by weight of dipentaerythritol hexacrylate (KAYARADDPHA of NIPPON KAYAKU Co., Ltd.), 5 parts by weight of radicalpolymerization initiator (IRGACURE 651 of Ciba Specialty Chemicals Co.,Ltd.), and 3 parts by weight of polyisocyanate compound (Coronate L ofNIPPON POLYURETHANE INDUSTRY CO., LTD) were added, and an ultravioletcuring type acrylic adhesive agent was prepared.

The adhesive agent was applied on one side of a soft vinyl chloride film(thickness 80 μm), and heated and dried, and an ultraviolet curing typeadhesive layer (thickness 5 μm) was formed. A separator (Lumirror S-10of Toray Industries CO., LTD, polyester film of 38 μm in thickness withpeeling treatment applied on the adhesive layer gluing side) was gluedto the adhesive layer, and a laminated sheet was manufactured. Thearithmetic average height (Ra) of the surface of the soft vinyl chloridefilm not contacting with the adhesive layer was 0.72 μm. The arithmeticaverage height (Ra) of the surface of the separator not contacting withthe adhesive layer was 0.03 μm.

The fabricated laminated sheet was taken up in roll, and a laminatedsheet roll was formed, and it was heated for 24 hours at 50° C. Afterheat treatment, the adhesive sheet for laser dicing (100 mm×100 mm) wascut out from the laminated sheet roll, and the arithmetic average height(Ra) of the surface of the soft vinyl chloride film not contacting withthe adhesive layer was measured, and the minimum value was 0.48 μm.

The adhesive sheet was glued to the polished side (reverse side) of thesilicon wafer, the base material surface of the adhesive sheet glued tothe silicon wafer was observed by laser microscope, and the surface wasfree from convex parts of width (W) of 20 mm or less and height (h) of 1μm or more, and concave parts of width (W) of 20 mm or less and depth(d) of 1 μm or more.

Example 2

In toluene, 70 parts by weight of butyl acrylate, 30 parts by weight of2-ethyl hexyl acrylate, and 5 parts by weight of acrylic acid werecopolymerized, and a solution containing acrylic polymer ofnumber-average molecular weight of 700,000 was obtained. In thissolution, 30 parts by weight of dioctyl phthalate, and 5 parts by weightof polyisocyanate compound (Coronate L of NIPPON POLYURETHANE INDUSTRYCO., LTD) were added, and an ultraviolet curing type acrylic adhesiveagent was prepared.

The adhesive agent was applied on one side of a soft vinyl chloride film(thickness 70 μm), and heated and dried, and an ultraviolet curing typeadhesive layer (thickness 10 μm) was formed. A separator (Lumirror S-10of Toray Industries CO., LTD, polyester film of 38 μm in thickness withpeeling treatment applied on the adhesive layer gluing side) was gluedto the adhesive layer, and a laminated sheet was manufactured. Thearithmetic average height (Ra) of the surface of the soft vinyl chloridefilm not contacting with the adhesive layer was 0.58 μm. The surface ofthe separator not contacting with the adhesive layer was roughened bysand blasting before gluing. The arithmetic average height (Ra) of thesurface was 0.33 μm.

The fabricated laminated sheet was taken up in roll, and a laminatedsheet roll was formed, and it was heated for 24 hours at 50° C. Afterheat treatment, the adhesive sheet for laser dicing (100 mm×100 mm) wascut out from the laminated sheet roll, and the arithmetic average height(Ra) of the surface of the soft vinyl chloride film not contacting withthe adhesive layer was measured, and the minimum value was 0.44 μm.

The adhesive sheet was glued to the polished side (reverse side) of thesilicon wafer, the base material surface of the adhesive sheet glued tothe silicon wafer was observed by laser microscope, and the surface wasfree from convex parts of width (W) or 20 mm or less and height (h) of 1μm or more, and concave parts of width (W) of 20 mm or less and depth(d) of 1 μm or more.

Example 3

An ultraviolet curing type acrylic adhesive agent was prepared in thesame manner as in example 1. The adhesive agent was applied on thesurface of poly-α-olefin film (thickness 80 μm) having corona treatmentapplied on one side, and heated and dried, and an ultraviolet curingtype adhesive layer (thickness 5 μm) was formed. A separator (LumirrorS-10 of Toray Industries CO., LTD, polyester film of 38 μm in thicknesswith peeling treatment applied on the adhesive layer gluing side) wasglued to the adhesive layer, and an adhesive sheet for laser dicing wasmanufactured. The arithmetic average height (Ra) of the surface of thepoly-α-olefin film not contacting with the adhesive layer was 0.55 μm.The arithmetic average height (Ra) of the surface of the separator notcontacting with the adhesive layer was 0.03 μm.

The adhesive sheet (100 mm×100 mm) was glued to the polished side(reverse side) of the silicon wafer, the base material surface of theadhesive sheet glued to the silicon wafer was observed by lasermicroscope, and the surface was free from convex parts of width (W) of20 mm or less and height (h) of 1 μm or more, and concave parts of width(W) of 20 mm or less and depth (d) of 1 μm or more.

Example 4

An ultraviolet curing type acrylic adhesive agent was prepared in thesame manner as in example 2. The adhesive agent was applied on thesurface of EVA film (thickness 115 μm) having corona treatment appliedon one side, and heated and dried, and an ultraviolet curing typeadhesive layer (thickness 10 μm) was formed. A separator (Lumirror S-10of Toray Industries CO., LTD, polyester film of 38 μm in thickness withpeeling treatment applied on the adhesive layer gluing side) was gluedto the adhesive layer, and an adhesive sheet for laser dicing wasmanufactured. The arithmetic average height (Ra) of the surface of theEVA film not contacting with the adhesive layer was 0.53 μm. Thearithmetic average height (Ra) of the surface of the separator notcontacting with the adhesive layer was 0.03 μm.

The adhesive sheet (100 mm×100 mm) was glued to the polished side(reverse side) of the silicon wafer, the base material surface of theadhesive sheet glued to the silicon wafer was observed by lasermicroscope, and the surface was free from convex parts of width (W) of20 mm or less and height (h) of 1 μm or more, and concave parts of width(W) of 20 mm or less and depth (d) of 1 μm or more.

Comparative Example 1

An ultraviolet curing type acrylic adhesive agent was prepared in thesame manner as in example 1. The adhesive agent was applied on one sideof soft vinyl chloride film (thickness 80 μm), and heated and dried, andan ultraviolet curing type adhesive layer (thickness 5 μm) was formed. Aseparator (Lumirror S-10 of Toray Industries CO., LTD, polyester film of38 μm in thickness with peeling treatment applied on the adhesive layergluing side) was glued to the adhesive layer, and a laminated sheet wasmanufactured. The arithmetic average height (Ra) of the surface of thesoft vinyl chloride film not contacting with the adhesive layer was 0.32μm. The arithmetic average height (Ra) of the surface of the separatornot contacting with the adhesive layer was 0.03 μm.

The fabricated laminated sheet was taken up in roll, and a laminatedsheet roll was formed, and it was heated for 24 hours at 50° C. Afterheat treatment, the adhesive sheet for laser dicing (100 mm×100 mm) wascut out from the laminated sheet roll, and the arithmetic average height(Ra) of the surface of the soft vinyl chloride film not contacting withthe adhesive layer was measured, and the minimum value was 0.20 μm.

The adhesive sheet was glued to the polished side (reverse side) of thesilicon wafer, the base material surface of the adhesive sheet glued tothe silicon wafer was observed by laser microscope, and the surfacecontained one convex part of width (W) of 20 mm or less and height (h)of 1 μm or more, and one concave part of width (W) of 20 mm or less anddepth (d) of 1 μm or more.

Comparative Example 2

An ultraviolet curing type acrylic adhesive agent was prepared in thesame manner as in example 2. The adhesive agent was applied on thesurface of EVA film (thickness 115 μm) having corona treatment appliedon one side, and heated and dried, and an ultraviolet curing typeadhesive layer (thickness 10 μm) was formed. A separator (Lumirror S-10of Toray Industries CO., LTD, polyester film of 38 μm in thickness withpeeling treatment applied on the adhesive layer gluing side) was gluedto the adhesive layer, and a laminated sheet was manufactured. Thearithmetic average height (Ra) of the surface of the EVA film notcontacting with the adhesive layer was 0.34 μm. The arithmetic averageheight (Ra) of the surface of the separator not contacting with theadhesive layer was 0.03 μm.

The fabricated laminated sheet was taken up in roll, and a laminatedsheet roll was formed, and it was heated for 24 hours at 50° C. Afterheat treatment, the adhesive sheet for laser dicing (100 mm×100 mm) wascut out from the laminated sheet roll, and the arithmetic average height(Ra) of the surface of the EVA film not contacting with the adhesivelayer was measured, and the minimum value was 0.18 μm.

The adhesive sheet was glued to the polished side (reverse side) of thesilicon wafer, the base material surface of the adhesive sheet glued tothe silicon wafer was observed by laser microscope, and the surfacecontained one convex part of width (W) of 20 mm or less and height (h)of 1 μm or more, and one concave part of width (W) of 20 mm or less anddepth (d) of 1 μm or more.

Reference Example 1

An ultraviolet curing type acrylic adhesive agent was prepared in thesame manner as in example 1. The adhesive agent was applied on thesurface of polyethylene film (thickness 80 μm) having corona treatmentapplied on one side, and heated and dried, and an ultraviolet curingtype adhesive layer (thickness 5 μm) was formed. A separator (LumirrorS-10 of Toray Industries CO., LTD, polyester film of 38 μm in thicknesswith peeling treatment applied on the adhesive layer gluing side) wasglued to the adhesive layer, and an adhesive sheet for laser dicing wasmanufactured. The arithmetic average height (Ra) of the surface of thepolyethylene film not contacting with the adhesive layer was 0.68 μm.The arithmetic average height (Ra) of the surface of the separator notcontacting with the adhesive layer was 0.03 μm.

The adhesive sheet (100 mm×100 mm) was glued to the polished side(reverse side) of the silicon wafer, the base material surface of theadhesive sheet glued to the silicon wafer was observed by lasermicroscope, and the surface was free from convex parts of width (W) of20 mm or less and height (h) of 1 μm or more, and concave parts of width(W) of 20 mm or less and depth (d) of 1 μm or more.

[Evaluation Tests]

The adhesive sheets manufactured in examples, comparative examples, andreference example were evaluated in the following tests.

(1) Tensile Test

A fabricated adhesive sheet was cut in a size of 10 mm in width and 100mm in length, and the stress in tensile state was measured by usingTensilon. The pulling speed was 300 mm/min.

As a result, in the adhesive sheets of examples 1 to 4 and comparativeexamples 1 and 2, the stress increased depending on the tensile amount,and an S-S curve rising rightward was obtained. On the other hand, inthe adhesive sheet of reference example 1, the stress dropped partially,and necking was observed.

(2) Expansion Test

A fabricated adhesive sheet was adhered to the polished side (reverseside) of the silicon wafer (thickness 50 μm), and the silicon wafer wasdiced by laser. As the laser, YAG laser with wavelength of 1064 mm wasused. By using a focusing lens, the light was focused into a spot insidethe silicon wafer. Then the silicon wafer was expanded by 20 mm by usingan expander. As a result, in examples 1 to 4, the small pieces ofelement were neatly separated completely, but in comparative examples 1and 2, small pieces of element were not separated partly. In referenceexample 1, the base material was torn apart, and small pieces of elementcould not be collected.

1. A method of manufacturing an adhesive sheet, comprising a step ofdisposing an adhesive layer on one side of a base material, a step offabricating a laminated sheet by stacking a separator on the adhesivelayer, a step of fabricating a rolled laminated sheet by taking up thelaminated sheet in roll, and a step of heating the rolled laminatedsheet at a temperature of 30 to 60° C. for 12 to 100 hours, wherein theresulting adhesive sheet has at least an adhesive layer on one side of abase material, wherein the base material has a surface having anarithmetic average height Ra of 0.4-0.9 μm, wherein said adhesive sheetis prepared by cutting said adhesive sheet from said rolled laminatedsheet, wherein the surface of the base material that does not contactthe adhesive layer is free from convex parts that have a height (h) of 1μm or more over a width (W) of 20 mm or less, and concave parts thathave a depth (d) of 1 μm or more over a width (W) of 20 mm or less, andwherein said separator comprises a surface not contacting with theadhesive layer that has an arithmetic average height Ra of 0.2 to 2 μm.2. The method of claim 1, wherein the arithmetic average height Ra ofthe surface of the base material not contacting with the adhesive layeris 0.4 μm or more.
 3. The method of claim 1, wherein the surface of theseparator not contacting with the adhesive layer is in sprinkled orrough structure.
 4. The method of claim 1, wherein the adhesive agentfor forming the adhesive layer is a radiation curing type adhesive. 5.The method of claim 1, wherein the base material is free from neckingproperty.
 6. The method of claim 1, wherein the base material containspolyvinyl chloride as resin component.
 7. The method of claim 1, whereinthe base material has substantially no heat deformation.
 8. The methodof claim 1, wherein said base material comprises flexible vinylchloride.
 9. A method of manufacturing small pieces of an elementcomprising a step of adhering an adhesive layer of an adhesive sheet forlaser dicing to one side of a workpiece, a step of forming a reformedregion in the workpiece by emitting laser beam, a step of dicing theworkpiece into individual chips by expanding the adhesive sheet forlaser dicing, and a step of peeling off the adhesive sheet for laserdicing from the separated workpiece, wherein the adhesive sheet forlaser dicing has at least an adhesive layer on one side of a basematerial, wherein the base material has a surface having an arithmeticaverage height Ra of 0.4-0.9 μm, wherein said adhesive sheet is preparedby: disposing a separator on the adhesive layer to form a laminatedsheet; taking up the laminated sheet in roll; heating the rolledlaminated sheet at a temperature of 30 to 60° C. for 12 to 100 hours;and said adhesive sheet is cut from said rolled laminated sheet, whereinthe surface of the base material that does not contact the adhesivelayer is free from convex parts that have a height (h) of 1 μm or moreover a width (W) of 20 mm or less, and concave parts that have a depth(d) of 1 μm or more over a width (W) of 20 mm or less, and wherein saidseparator comprises a surface not contacting with the adhesive layerthat has an arithmetic average height Ra of 0.2 to 2 μm.
 10. The methodof claim 9, wherein the arithmetic average height Ra of the surface ofthe base material not contacting with the adhesive layer is 0.4 μm ormore.
 11. The method of claim 9, wherein the surface of the separatornot contacting with the adhesive layer is in sprinkled or roughstructure.
 12. The method of claim 9, wherein the adhesive agent forforming the adhesive layer is a radiation curing type adhesive.
 13. Themethod of claim 9, wherein the base material is free from neckingproperty.
 14. The method of claim 9, wherein the base material containspolyvinyl chloride as resin component.
 15. The method of claim 9,wherein the base material has substantially no heat deformation.
 16. Themethod of claim 9, wherein said base material comprises flexible vinylchloride.